Antireflection film

ABSTRACT

An antireflection film comprises a transparent substrate carrying on one surface a polymeric antireflection layer, this antireflection layer having a refractive index at least about 0.02 lower than that of the substrate and being formed from a cured polymer comprising repeating units derived from a fluoroalkene, an alkyl acrylate or methacrylate and a polyfunctional acrylate monomer. No inorganic antireflection layer is present between the substrate and the polymeric antireflection layer.

REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.09/026,271, filed Feb. 19, 1998, pending.

BACKGROUND OF THE INVENTION

This invention relates to an antireflection film comprising a polymericsubstrate bearing a polymeric antireflection layer, and to a process forproducing such an antireflection film.

It has long been known that it is advantageous to provide variousarticles, for example lenses, cathode ray tubes, flat panel displays,window films and windshields, with antireflection films which reduce theamount of light reflected from the surface of the article and thusreduce or eliminate “ghost” images formed by such reflected light Forexample, U.S. Pat. Nos. 5,106,671; 5,171,414 and 5,234,748 describeantireflection films which are placed on the inside surface ofautomobile windshields to reduce the intensity of the image of theinstrument panel caused by light reflected from the inside surface ofthe windshield.

Antireflection coatings on a substrate typically comprise a plurality ofinorganic layers, for example a metal or metal oxide layer and a silicalayer. (The term “silica” is used herein in accordance with its normalmeaning in the antireflection art to mean a material of the formulaSiO_(x) where x is not necessarily equal to two. As those skilled in theart are aware, such silica layers are often deposited by chemical vacuumdeposition or sputtering of silicon in an oxygen atmosphere, so that thematerial deposited does not precisely conform to the stoichiometricformula SiO₂ of pure silica.) Typically, one surface of a silica layeris exposed, and this exposed surface, which has a high surface energy,as shown by its low contact angle with water, is highly susceptible tofingerprints and other marks. Such marks are extremely difficult toclean, often requiring the use of chemical cleaners.

Perhaps the most effective antireflection film available commercially isthat sold by Southwall Technologies, 1029 Corporation Way, Palo Alto,Calif. 94303. This material comprises a 180 μm poly(ethyleneterephthalate) substrate provided with an abrasion-resistant hard coat,and then successively with a 17 nm indium tin oxide (ITO) layer, a 23 nmsilica layer, a 95 nm ITO layer, an 84 nm silica layer and finally athin “lubrication” layer, which is formed from a fluoropolymer and isstated to improve the scratch resistance and the susceptibility of thesurface to marking.

This complex film possesses excellent antireflection characteristics,but is so expensive (approximately US$10 per square foot, US$100 m⁻²) asto preclude its use in many applications where antireflection films aredesirable. Much of the high cost of this film can be attributed to the95 nm ITO layer and 84 nm silica layer; since these layers are typicallyformed by sputtering, and the cost of a sputtered layer is directlyproportional to its thickness. Furthermore, if it is desired to producelarge quantities of such a complex film on a production line basis, theneed for four separate sputtering stations, all of which must bemaintained under high vacuum, results in a complex and costly apparatus.

For example, the aforementioned multilayer antireflection coatings aretoo expensive for use on photographic images. It has long been knownthat the appearance of photographs and other images can be improved byproviding an antireflection coating over the image. For example, U.S.Pat. Nos. 3,793,022 and 3,925,081 describe peel-apart diffusion transferphotographic units in which the surface of the image-receiving elementthrough which the final photograph is viewed (hereinafter called the“viewing surface”) is provided with an antireflection layer comprising afluorinated polymer. Preferably the fluorinated polymer also includes anisocyanate to improve the abrasion resistance of the antireflectionlayer. Similarly, U.S. Pat. No. 4,047,804 describes peel-apart diffusiontransfer photographic units in which the viewing surface is providedwith an antireflection layer comprising a fluorinated polymerincorporating a polydimethylsiloxane. U.S. Pat. Nos. 4,904,525 and4,940,602 describe an optical article comprising a transparent plasticsubstrate; a hard coat film formed on a surface of the substrate, thefilm having an index of refraction of not less than 1.52; and afluorine-containing organopolysiloxane-based film with a thickness of 10nm to 500 nm, which has an index of refraction lower than that of thehard coat film by not less than 0.02, and which is formed on the hardcoat film.

U.S. Pat. Nos. 5,061,769; 5,178,955; and 5,225,244 describe solid bodieshaving a reflective surface and provided with an antireflection coatingof a terpolymer composition derived from (a) perfluoroalkylalkylacrylate or methacrylate, (b) acrylic, methacrylic or itaconic acid, and(c) hydroxyl-containing acrylate or methacrylate. Among the solid bodiesmentioned in these patents are optical lenses; eyeglasses, both plasticand glass; windows, glass as well as polymeric windows, such as windowsof clear polymeric vinyl (including copolymers thereof), styrene,acrylics or polycarbonate; clear polymer films such as vinyl (includingcopolymers), nylon, polyester, and the like; the exterior viewingsurface of liquid crystal displays, cathode ray tubes (e.g. videodisplay tubes for televisions and computers); and the like; and thesurface of glossy displays and pictures, such as glossy prints andphotographs.

The selection of materials for use in antireflection coatings on plasticfilms and similar substrates is affected by numerous factors. Theantireflection coating needs to have a lower refractive index than theplastic substrate in order to reduce surface reflections substantially.However, the antireflection coating must also adhere firmly to thesubstrate, be sufficiently transparent that it, does not affect theappearance of the underlying image, and have good scratch resistance andimpact resistance. In addition, it is highly desirable that theantireflection coating have good anti-static properties, be flexible sothat it does not affect the mechanical properties of the substrate andbe resistant to water and common solvents to which it may be exposed.Some of these desirable characteristics of antireflection coatings tendto conflict with one another; for example, highly fluorinated coatingshave low refractive indices, but tend to be too soft and lack sufficientadherence to other polymers for optimum performance as antireflectioncoatings.

The aforementioned parent application Ser. No. 09/026,271 describesmultilayer antireflection coatings comprising one or more inorganicantireflection layers and a top layer of a polymer having a refractiveindex not greater than about 1.53 over the wavelength range of 400 to700 nm and a thickness of from about 20 to about 200 nm. In a preferredembodiment of this multilayer antireflection coating, the polymer layeris formed from a terpolymer comprising repeating units derived from afluoroalkene, an alkyl acrylate or methacrylate and a polyfunctionalacrylate monomer. It has now been found that this terpolymer can be usedalone, without an inorganic antireflection layer, to provide a low cost,but effective, antireflection coating on polymeric and other transparentsubstrates. The resultant antireflection coatings have desirableproperties and are especially useful on polymeric films used in theimage-receiving elements of diffusion transfer photographic units.

SUMMARY OF THE INVENTION

Accordingly, this invention provides an antireflection film comprising asubstantially transparent substrate bearing a polymeric antireflectionlayer, which forms one outer surface of the antireflection film. Theantireflection layer has a refractive index at least about 0.02 lessthan that of the substrate over the wavelength range of 400 to 700 nm.The antireflection layer is formed from a cured polymer comprisingrepeating units derived from a fluoroalkene, an alkyl acrylate ormethacrylate and a polyfunctional acrylate monomer; there is noinorganic antireflection layer present between the substrate and thepolymeric antireflection layer.

This invention also provides a process for providing a polymericantireflection film on a substantially transparent substrate, thissubstrate being free from inorganic antireflection layers. This processcomprises depositing a layer of a curable composition on the substrate,the curable composition comprising a polymer of a fluoroalkene, apolymer of an alkyl acrylate or methacrylate, and a polyfunctionalacrylate monomer, and effecting free radical curing of the depositedcurable composition to form a polymeric antireflection layer having arefractive index at least about 0.02 less than that of the substrateover the wavelength range of 400 to 700 nm.

This invention also provides an image-receiving element adapted toreceive dye and thereby form an image, the image-receiving elementcomprising:

a substantially transparent polymeric substrate;

an image-receiving layer disposed on the polymeric substrate andcontaining at least one mordant for a dye; and

a polymeric antireflection layer disposed on the opposed surface ofsubstrate from the image-receiving layer and having a refractive indexat least about 0.02 less than that of the substrate over the wavelengthrange of 400 to 700 nm, the antireflection layer being formed from acured polymer comprising repeating units derived from a fluoroalkene, analkyl acrylate or methacrylate and a polyfunctional acrylate monomer.

This invention also provides a photographic product for forming adiffusion transfer image and comprising:

a photosensitive element comprising at least one photosensitive layerhaving associated therewith an image dye-providing material, thephotosensitive element being such that upon its exposure to light andcontact with an alkaline developing composition, an image dye isreleased from non-exposed regions of the photosensitive element; and

an image-receiving element superposed on the photosensitive element soas to receive image dye released from the photosensitive element andthereby form an image, the image-receiving element bearing, on itssurface remote from the photosensitive element, a polymericantireflection layer having a refractive index at least about 0.02 lessthan that of the substrate over the wavelength range of 400 to 700 nm,the antireflection layer being formed from a cured polymer comprisingrepeating units derived from a fluoroalkene, an alkyl acrylate ormethacrylate and a polyfunctional acrylate monomer.

Finally, this invention provides an image display device comprisingmeans for receiving data representing an image, and a screen capable ofgenerating light to produce a visual image corresponding to the datareceived by the data receiving means, the screen having an outer surfacethrough which the visual image can be viewed. The outer surface of thescreen is provided with a polymeric antireflection layer having arefractive index at least about 0.02 less than that of the screen overthe wavelength range of 400 to 700 nm. This antireflection layer isformed from a cured polymer comprising repeating units derived from afluoroalkene, an alkyl acrylate or methacrylate and a polyfunctionalacrylate monomer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 of the accompanying drawing shows a reflectance curve for a firstpreferred antireflection film of the present invention comprising apreferred terpolymer on a “bare” poly(ethylene terephthalate) (PET)substrate, as prepared in Example 1 below;

FIG. 2 shows a reflectance curve for a second preferred antireflectionfilm of the present invention comprising the same terpolymer on a PETsubstrate bearing an acrylic hard coat, as prepared in Example 2 below;and

FIG. 3 shows a reflectance curve for a third preferred antireflectionfilm of the present invention comprising the same terpolymer on apolyphenylene substrate, as prepared in Example 3 below.

DETAILED DESCRIPTION OF THE INVENTION

As already indicated, the present invention provides an antireflectionfilm comprising a substantially transparent substrate bearing apolymeric antireflection layer, there being no inorganic antireflectionlayers between the substrate and the polymeric antireflection layer. Asdescribed in more detail below, the substrate may be provided, on one orboth surfaces, with a conventional hard coat before the antireflectionlayer is applied; thus, a hard coat may be present between the substrateand the antireflection layer. The antireflection layer has a refractiveindex at least about 0.02 less than that of the substrate over thevisible wavelength range of 400 to 700 nm, and comprises repeating unitsderived from a fluoroalkene, an alkyl acrylate or methacrylate and apolyfunctional acrylate monomer (“polyfunctional” being used herein inits conventional sense to denote a material having a functionality of 3or higher).

The substrate of the present film can be any material on which anantireflection coating is desired, provided of course that the substratecan withstand the (relatively mild) conditions needed for formation ofthe antireflection layer and provided that the substrate has asufficiently high refractive index for the antireflection layer tofulfil properly its antireflection function. As will readily be apparentto those skilled in the art of antireflection coatings, in saying thatthe substrate is “substantially transparent” we do not exclude thepossibility that the substrate may have some haze or color or similardeviation from ideal transparency, provided that the substrate permits aviewer to see material behind the substrate. Furthermore, although thesubstrate itself needs to be substantially transparent, the substratemay form only part of a larger article which includes non-transparentlayers. Thus, the substrate might form part of a photograph, and bebacked by a dye layer containing an image and a diffuse reflectinglayer.

As is well known to those skilled in antireflection coatings, theantireflection properties of a coating on a substrate increase withdifference in refractive index between the coating and the substrate.Thus, although in the antireflection film of the present invention, theantireflection coating must have a refractive index at least about 0.02less than that of the substrate over the visible wavelength range of 400to 700 nm, in general, it is desirable that this difference inrefractive index be at least about 0.05 (and preferably more) over thiswavelength range. Since the refractive indices of the polymers used toform the antireflection layers in the present invention typically haverefractive indices of about 1.50 to about 1.53, to provide a relativelylarge difference between the refractive indexes of the antireflectionlayer and the substrate, it is desirable that the substrate have arefractive index of at least about 1.60 over the wavelength range of 400to 700 nm.

Although other substrates may the used, the substrate will typically beeither an organic polymer or a glass. One specific preferred type oforganic polymeric substrate is polyester; suitable polyester films arereadily available commercially, for example the 4 to 7 mil (101 to 177μm) poly(ethylene terephthalate) films sold under the registeredtrademark “MELINEX” by ICI Americas Inc., Wilmington, Del. Suchpolyesters typically have refractive indices of about 1.65. Anotherpreferred polymeric substrate is a polyphenylene polymer, for examplethose sold under the trademark “PARMAX” by Maxdem Incorporated, 140 EastArrow Highway, San Dimas, Calif. 91773-3336. These polyphenylenepolymers have high refractive indices of about 1.69, and thus an highlyeffective antireflection layer can readily be formed thereon. Thesepolyphenylene polymers also have the advantage of being both flexibleand scratch-resistant, so that the anti-reflection layer can alsoprovide scratch resistance to the substrate.

As already indicated, the polymeric substrate may be provided withcoatings on one or both surfaces to improve its hardness and scratchresistance, to improve the adhesion of the antireflection layer to thesubstrate, or to provide any other desired properties, for examplefiltration of ultra-violet radiation or provision of a gas and/ormoisture barrier. A hard coating on the substrate, which should have ahigher refractive index than the substrate to improve the antireflectionproperties of the antireflection layer, will typically have a thicknessof about 1 to about 15 μm, preferably from about 2 to about 3 μm, andsuch a hard coating may be provided by free radical polymerization(initiated either thermally or by ultra-violet radiation) of anappropriate polymerizable material. An especially preferred hard coatfor use in the present invention is the acrylic polymer coating soldunder the trademark “TERRAPIN” by Tekra Corporation, 6700 West LincolnAvenue, New Berlin, Wis. 53151.

Although (at least in theory), the antireflection layer of the presentfilm might be produced in other ways, it is preferred that thisantireflection layer be formed on the polymeric substrate by depositinga layer of a curable composition and then curing this layer in situ. Therelatively thin layer of curable composition required can be appliedwith good uniformity by solution coating or other conventional coatingtechniques. Obviously, the deposition of the layer of curablecomposition, and its subsequent curing, should be effected underconditions which do not cause damage to the polymeric substrate; theseconditions of course vary with the exact polymeric substrate employed.

The curable composition may be cured by any conventional method, but isdesirably cured by a free radical curing, which may be initiated eitherthermally or by ultra-violet radiation, although the latter is generallypreferred. Persons skilled in polymer technology will be familiar withappropriate initiators, oxygen scavengers and other components useful insuch free radical curing. However, it should be noted that, because ofthe extreme thinness of the polymeric antireflection layer desired inthe present film, the type and proportion of initiator(s) required maydiffer from typical formulations intended for production of thickerpolymer layers.

As already indicated, the antireflection layer in the film of thepresent invention typically has a refractive index not greater thanabout 1.53 over the wavelength range of 400 to 700 nm. The optimumthickness of the antireflection layer for any particular combination ofmaterials in the substrate and the antireflection layer may bedetermined by routine empirical tests or by theoretical calculations,both of which will be familiar to those skilled in the art of designingantireflection films. In general, the antireflection layer desirably hasa thickness of from about 20 to about 200 nm, preferably about 60 toabout 130 nm. Polymeric antireflection layers having thicknesses withinthese ranges are readily prepared by depositing a solution of anappropriate curable composition in an organic solvent using conventionalsolution coating techniques, for example slot coating, removing thesolvent and curing the resultant layer of curable material.

It is desirable to keep the refractive index of the polymerantireflection layer as low as possible consistent with other acceptableproperties for this layer, especially hardness and scratch and stainresistance. The polymer should also be resistant to cleaning solventswhich may be used on the film, for example ethyl alcohol, aqueousammonia, acetone, gasoline and isopropanol, and food and cosmetic items,for example peanut butter and lipstick with which it may come intocontact. Finally, the polymer should also have good durability, asmeasured, for example by its ability to withstand rubbing with steelwool. Desirably, the polymer layer has a refractive index below about1.50 over the entire visible range of 400 to 700 nm. To provide asuitably low refractive index, the repeating units derived from afluoroalkene in the polymeric antireflection layer are preferablyderived from vinylidene fluoride and/or tetrafluoroethylene. This, thecurable composition used to form the polymeric antireflection layerdesirably comprises a polymer of a fluoroalkene, for examplepoly(vinylidene fluoride) or a vinylidene fluoride/tetrafluoroethylenecopolymer, such as the material sold under the trademark “KYNAR” by SanDiego Plastics, Inc., 2220 McKinley Avenue, National City, Calif. 91950.To provide the polymeric antireflection layer with good scratchresistance, it is desirable that the repeated units derived from analkyl acrylate or methacrylate be derived from methyl methacrylate, andthus that the curable composition include a poly(methyl methacrylate),such as the material sold under the trademark “ELVACITE 2041” by ICIAcrylics, Inc., 3411 Silverside Road-McKean 2nd, Wilmington, Del.19850-5391, or that sold under the trademark “ACRYLOID A21” by Rohm andHaas, 100 Independence Mall West, Philadelphia, Pa. 19106-2399. Topromote cross-linking within the polymeric antireflection layer, andthus increase the hardness of this layer, a specific preferredpolyfunctional acrylate monomer is that sold under the trademark “SR399” by Sartomer, Inc., 502 Thomas Jones Way, Exton, Pa. 19341; thismaterial is stated by the manufacturer to be dipentaerythritolpentaacrylate.

It is well known to those skilled in polymer science that most polymershave a negative dispersion with the visible range, i.e., theirrefractive index at 700 nm is smaller than their refactive index at 400nm. Calculations show that such negative dispersion adversely affectsthe antireflection properties of the film and hence it is desirable toreduce such negative dispersion as far as possible. The aforementionedKYNAR polymer has a low refractive index and small negative dispersion,which render it very suitable for use in the present antireflectionlayer. While the desirability of a fluoroalkene polymer to provide lowrefractive index in the polymer layer and for an acrylate ormethacrylate cross-linker to provide hardness in the same layer mightsuggest that the properties of the polymer layer must inevitably involvea compromise between the two properties, it has been found that, if theformulation of the curable composition is carefully chosen, segregationof material occurs spontaneously during curing, resulting in a polymerlayer having an outer portion enriched in the acrylate or methacrylatepolymer (and thus of enhanced hardness) and an inner portion enriched inthe fluoroalkene polymer (and thus of reduced refractive index). Anadditional benefit of such segregation of acrylate or methacrylatepolymer material during curing is that, under certain circumstances, itenables the cross-linking to occur in an oxygen-containing atmosphere,such as air, thereby avoiding the need for a nitrogen blanket as iscustomary during thin film ultra-violet curing, and thus reducing thecost of manufacture of the antireflection film.

The finished antireflection film of the present invention, having theantireflection coating formed thereon, may be applied to, for example, acathode ray tube, a flat panel display, window glass or a windshield,which it is desired to provide with antireflection characteristics.However, as already indicated, the antireflection film is especiallyusefull in image-receiving elements, such as those used inself-developing photographic film units. Such image-receiving elementstypically comprise a substantially transparent polymeric substrate, andan image-receiving layer disposed on one surface of the polymericsubstrate and containing a mordant for one or more dyes which theimage-receiving elements receives in order to form an image. This imageis usually viewed through the polymeric substrate. Accordingly, byproviding the surface of this substrate opposed to that on which theimage-receiving layer is disposed with a polymeric antireflection layerof this invention, the antireflection properties of this surface can beimproved, with consequent improvement in the apparent quality of theimage. The antireflection film of the present invention is sufficientlyinexpensive to be useful in such image-receiving elements, whereas themore elaborate antireflection films described above containing multipledielectric layers are too expensive to be practicable in this use.

This invention extends to a photographic product for forming a diffusiontransfer image and comprising an image-receiving element of the presentinvention as described in the preceding paragraph, in conjunction with aconventional photosensitive element for producing a diffusion transferimage,

The antireflection films of the present invention are also useful inimage display devices, for example cathode ray tubes, liquid crystaldisplays, gas plasma displays and others. The outer surface of suchimage display devices through which the image is viewed will typicallybe formed from either glass or a plastic. The antireflection film may bea separate plastic film provided with an antireflection layer and thenapplied to the glass or plastic outer surface of the display device.Alternatively, the antireflection layer may be formed directly on theglass or plastic front surface.

The antireflection film of the present invention may be especiallyuseful when applied to so-called “flat screen” cathode ray tubesintended for use in computer monitors. It is well-known that, to enhancethe contrast of such a cathode ray tube, it is necessary to provide adark color to the display surface thereof. In traditional curved screencathode ray tubes, the necessary dark color has been provided by tintingthe glass; such an approach is practicable in curved screen tubes sincethe thickness of the glass is essentially constant throughout, so thatthe tint in the glass produces the same dark color over the wholedisplay surface. However, so-called “flat screen” cathode ray tubes arenow being introduced in which the entire front surface is essentiallyflat. In such flat screen tubes, the thickness of the glass varies overthe display surface, being thicker near the edges than in the center ofthe screen. Accordingly, it is not possible to use tinted glass toprovide the dark color needed in such flat screen tubes, since thevariation in the thickness of the glass would result in the darkness ofthe screen varying over the display surface. The desired dark screencolor may, however, be provided by applying to the glass anantireflection film of the present invention having at least one coloredlayer therein. This colored layer may, for example, be provided byincorporating into the anti-reflection film a tinted polymericsubstrate. a tinted hard coat or a colored layer separate from the allthe other layers of the film and serving solely to provide the necessarytint.

Preferred embodiments of the present invention will now be described,though by way of illustration only, to show preferred reagents,conditions and techniques used in the present process.

EXAMPLE 1

A liquid curable composition was prepared having the followingcomposition (the proportions are by dry weight of the solution):

% by weight Poly(vinylidene fluoride) (KYNAR) 46.8 Methyl methacrylate(ACRYLOID A21) 6.9 Dipentaerythritol pentaacrylate (Sartomer SR 399)30.7 Multifunctional acrylate monomer (Sartomer CD9051) 3.0 Coatingadditive (COATOSIL 3503¹) 4.0 Adhesion promoter (SILANE A174¹) 1.0Curing initiator (DARACURE 1173²) 2.0 Curing initiator (QUANTACURE BMS³)4.0 Oxygen scavenger (DIDMA⁴) 1.6 Notes: ¹Both available from OSiSpecialties, 39 Old Ridgebury Road, Danbury, Connecticut 06810-5121.²Available from Ciba-Geigy Corporation, 540 White Plains Road, P.O. Box2005, Tarrytown, New York 10591-9005. ³Manufactured by Great LakesChemical Corporation, and available from Biddle Sawyer Corporation, 2Penn Plaza, New York, New York 10121. ⁴Available from Aldrich ChemicalCompany, 1001 West St. Paul, Milwaukee, Wisconsin 53233.

The various components were prepared as stock solutions in methyl ethylketone (MEK), at 20 percent w/w, except that the ACRYLOID A21 andQUANTACURE BMS were prepared at 10 percent w/w, and the DARACURE andDIDMA were prepared at 5 percent w/w. The requisite quantities of thevarious stock solutions were then mixed, together with sufficientadditional MEK to give 2000 g of a coating solution containing 2.75percent solids w/w.

This coating solution was then applied via a slot coater to one surfaceof a “bare” 4 mil (101 μm) PET film, the solvent was allowed toevaporate and the film was placed under an ultra-violet lamp to cure thepolymer to produce a polymeric antireflection layer approximately 94 nmthick. The reflectance of the resultant antireflection film was thenmeasured on three samples over the wavelength range of 400-750 nm usinga ultraviolet/visible spectrophotometer (Perkin-Elmer Model Lambda 40P,available from The Perkin-Elmer Corporation, 761 Main Avenue, Norwalk,Conn. 06859-0001). The results are shown in FIG. 1 of the accompanyingdrawings, which also shown the reflectance curve for the bare PET filmused. The photopic reflectance value for the PET bearing theantireflection layer (measured according to CIE 1931, which specifies aweighted average of the reflectance over the spectral range of 450 to650 nm centered at 550 nm and weighted mostly highly at this wavelength)was 1.86%, as opposed to 6.02% for the bare PET. The antireflectionlayer exhibited good resistance to scratching with steel wool orfingerprinting. The layer had a contact angle with water ofapproximately 89°.

EXAMPLE 2

Example 1 was repeated, except that, prior to the deposition of thepolymeric antireflection layer, the surface of the PET which was to bearthe antireflection layer was coated with a 4 μm acrylic hard coat ofrefractive index 1.522 using an ultraviolet-curable polyfunctionalacrylate ester available commercially from Courtaulds Performance Films,P.O. Box 5068, Martinsville, Va. 24115. The reflectance of the finalfilm was tested in the same way as in Example 1 above, and the resultsobtained from three samples of the film are shown in FIG. 2. Thephotoptic reflectances for the three samples of PET bearing theantireflection layer were 2.46, 2.57 and 2.69% respectively, as opposedto 4.47% for the hard-coated PET alone.

EXAMPLE 3

Example 1 was repeated, except that the PET substrate was replaced by asubstrate of polyphenylene (Parmax 1000, sold commercially by Maxdem)refractive index 1.69. The reflectance of the final film was tested inthe same way as in Example 1 above, and the results are shown in FIG. 3.

It will be apparent to those skilled in the relevant art that numerouschanges and modifications can be made in the preferred embodiment of theinvention described above without departing from the scope of theinvention.

What is claimed is:
 1. An antireflection film comprising a substantiallytransparent substrate bearing a polymeric antireflection layer, theantireflection layer forming one outer surface of the antireflectionfilm and having a refractive index at least approximately 0.02 less thanthat of the substrate over the wavelength range of 400 to 700 nm, theantireflection layer being formed from a cured polymer comprisingrepeating units derived from a fluoroalkene, an alkyl acrylate ormethacrylate and a polyfuctional acrylate monomer, there being noinorganic antireflection layer present between the substrate and thepolymeric antireflection layer.
 2. An antireflection film according toclaim 1 wherein the antireflection layer has a refractive index at leastapproximately 0.05 less than that of the substrate over the wavelengthrange of 400 to 700 nm.
 3. An antireflection film according to claim 1wherein the substrate has a refractive index of at least approximately1.60 over the wavelength range of 400 to 700 nm.
 4. An antireflectionfilm according to claim 1 wherein the substrate comprises an organicpolymer.
 5. An antireflection film according to claim 4 wherein theorganic polymer is a polyester or a polyphenylene polymer.
 6. Anantireflection film according to claim 5 wherein the polymer comprisespoly(ethylene terephthalate).
 7. An antireflection film according toclaim 1 wherein the substrate comprises glass.
 8. An antireflection filmaccording to claim 1 having a hard coat disposed between the substrateand the polymeric antireflection layer, the hard coat having arefractive index higher than that of the substrate.
 9. An antireflectionfilm according to claim 1 wherein the polymeric antireflection layercomprises repeating units derived from vinylidene fluoride and/ortetrafluoroethylene.
 10. An antireflection film according to claim 1wherein the polymeric antireflection layer comprises repeating unitsderived from methyl methacrylate.
 11. An antireflection film accordingto claim 1 wherein the polymeric antireflection layer comprisesrepeating units derived from dipentaerythritol pentaacrylate.
 12. Anantireflection film according to claim 1 wherein the polymericantireflection layer has a thickness in the range of from about 20 toabout 200 nm.
 13. An antireflection film according to claim 12 whereinthe polymeric antireflection layer has a thickness in the range of fromabout 60 to about 130 nm.
 14. An antireflection film according to claim1 wherein the polymeric antireflection layer has an outer portionenriched in the alkyl acrylate or methacrylate and an inner portionenriched in the fluoroalkene.
 15. A process for providing a polymericantireflection film on a substantially transparent substrate, thesubstrate being free from inorganic antireflection layers, the processcomprising: depositing a layer of a curable composition on thesubstrate, the curable composition comprising a polymer of afluoroalkene, a polymer of an alkyl acrylate or methacrylate, and apolyfunctional acrylate monomer; and effecting free radical curing ofthe deposited curable composition to form a polymeric antireflectionlayer having a refractive index at least approximately 0.02 less thanthat of the substrate over the wavelength range of 400 to 700 nm.
 16. Aprocess according to claim 15 further comprising depositing a hard coaton the substrate before the polymeric antireflection layer is depositedthereon, the hard coat having a refractive index higher than that of thesubstrate, the curable composition being deposited on top of the hardcoat.
 17. A process according to claim 15 wherein the curing of thecurable composition is conducted in air.
 18. A process according toclaim 15 wherein the substrate has a refractive index of at leastapproximately 1.60 over the wavelength range of 400 to 700 nm.
 19. Aprocess according to claim 15 wherein the substrate comprises an organicpolymer.
 20. A process according to claim 19 wherein the organic polymeris a polyester or a polyphenylene polymer.
 21. A process according toclaim 20 wherein the polymer comprises poly(ethylene terephthalate). 22.A process according to claim 15 wherein the substrate comprises glass.23. A process according to claim 15 wherein the curable compositioncomprises a polymer of vinylidene fluoride and/or tetrafluoroethylene.24. A process according to claim 15 wherein the curable compositioncomprises dipentaerythritol pentaacrylate.
 25. A process according toclaim 15 wherein the polymeric antireflection layer formed has athickness in the range of from about 20 to about 200 nm.
 26. A processaccording to claim 25 wherein the polymeric antireflection layer formedhas a thickness in the range of from about 60 to about 130 nm.
 27. Animage-receiving element adapted to receive dye and thereby form animage, the image-receiving element comprising: a substantiallytransparent polymeric substrate; an image-receiving layer disposed onthe polymeric substrate and containing at least one mordant for a dye;and a polymeric antireflection layer disposed on the opposed surface ofsubstrate from the image-receiving layer and having a refractive indexat least approximately 0.02 less than of the polymeric substrate overthe wavelength range of 400 to 700 nm, the antireflection layer beingformed from a cured polymer comprising repeating units derived from afluoroalkene, an alkyl acrylate or methacrylate and a polyfunctionalacrylate monomer.
 28. A photographic product for forming a diffusiontransfer image and comprising: a photosensitive element comprising atleast one photosensitive layer having associated therewith an imagedye-providing material, the photosensitive element being such that uponits exposure to light and contact with an alkaline developingcomposition, an image dye is released from non-exposed regions of thephotosensitive element; and an image-receiving element in superposedrelationship with the photosensitive element so as to receive image dyereleased from the photosensitive element and thereby form an image, theimage-receiving element bearing, on its surface remote from thephotosensitive element, a polymeric antireflection layer having arefractive index at least approximately 0.02 less than that of theimage-receiving element over the wavelength range of 400 to 700 nm, theantireflection layer being formed from a cured polymer comprisingrepeating units derived from a fluoroalkene, an alkyl acrylate ormethacrylate and a polyfunctional acrylate monomer.
 29. An image displaydevice comprising: means for receiving data representing an image; and ascreen capable of generating light to produce a visual imagecorresponding to the data received by the data receiving means, thescreen having an outer surface through which the visual image can beviewed, the outer surface of the screen being provided with a polymericantireflection layer having a refractive index at least approximately0.02 less than that of the screen over the wavelength range of 400 to700 nm, the antireflection layer being formed from a cured polymercomprising repeating units derived from a fluoroalkene, an alkylacrylate or methacrylate and a polyfunctional acrylate monomer.